Scatter, SID and OID Flashcards
1
Q
What is scatter?
A
- Radiation from the primary beam
- Forward scatter (fogging)
- Backward scatter
- Absorbed scatter
2
Q
How is scatter reduced?
A
- Minimal kV
- Collimate the primary beam
- Compression to reduce tissue thickness
- Using grids to reduce fogging
- Table covered with 1mm lead to reduce back scatter
3
Q
What are grids?
A
- Strips that absorb scattered X-rays
- Need to increase mAs if using
- Improves image but not safety
4
Q
When do grids need to be used?
A
- If tissue if over 10cm thick
- Can be placed between patient and film or may be integral within X-ray table
5
Q
What are the 4 different grids?
A
- Stationary (parallel): cheapest
- Stationary (focused):
- Moving (Potter-Bucky grid)
- Digital: software analyses the image for scatter and removes it without a physical grid
6
Q
What does SID stand for?
A
- Source-image distance
7
Q
What does OID stand for?
A
- Object-image distance
8
Q
What is the penumbra effect?
A
- The bigger the area of X-ray production, the more pathways X-rays can travel along, so X-rays hit the film in different angles, which blurs edges
9
Q
What will happen if the SID is too large?
A
- Intensity which reaches the imaging plate is reduced, so compensation is needed by increasing mAs
10
Q
What will happen if the SID is too small?
A
- X-rays become more divergent, so penumbra effect is increased
11
Q
What will happen if the OID is too large?
A
- The primary beam continues to diverge after passing through the object, which will lead to distortion and greater penumbra effect due to magnification
12
Q
How is image distortion limited?
A
- Limit scatter
- Limit penumbra
- Limit magnification
- Limit movement blur
13
Q
How can the radiographer minimise their exposure to scatter?
A
- Wear a lead impregnated apron
- Stand behind a lead impregnated screen
- Stand at least 2m from primary beam
- Sedate animal and use positioning aids to preclude holding
- Rotate personel
- Dosimetry badges to monitor exposure
